Bring a large pot of lightly salted water to a boil. Add the pasta, and cook for 8 to 10 minutes, until tender. Drain and cool, then transfer to a large bowl.
In a blender or large food processor, combine the vinegar, sugar, mustard, garlic powder, salt, pepper, parsley, onion and cucumber. Puree until it forms a smooth sauce, about 3 minutes.
Pour over the pasta, and stir to coat evenly. Cover, and refrigerate for 3 days before serving. Stir once a day.
